The present invention relates to a projection aligner that transfers a pattern formed on a mask to an object to be exposed by scanning a light beam across the mask and the object.
Projection aligners have been used to form wiring patterns of PCBs (Printed Circuit Boards), for example. Such projection aligners typically include light sources emitting light beams toward the mask, projection optical systems for projecting respective light beams passed through the mask to the object such as the substrate of the PCB, and a driving mechanism that moves the mask and the object such that the light beams scan across the mask and the object.
Since the size of the object changes due to, for example, temperature variation of the atmosphere, the projection aligner is configured so as to be capable of adjusting the size of the image of the mask pattern projected onto the object in accordance with the size change of the object, so that the image can be transferred to a correct location on the object.
The size of the image is magnified by changing the magnification of the projection optical system as well as adjusting the velocities of the mask and the object moved by the driving mechanism. If the image of the mask pattern transferred to the object should be enlarged for 1%, for example, the projection optical system is adjusted at xc3x971.01 magnification and the mask and the object are moved so that the velocity of the object is 1% higher than that of the mask.
In many cases, however, the expansion/contraction ratio of the object varies with direction. For example, the expansion/contraction ratios in the direction in which the light beams are scanned over the object (which will be referred to hereinafter as xe2x80x9cbeam scanning directionxe2x80x9d), and in the direction perpendicular to the beam scanning direction are often not the same. In such cases, in order to transfer the mask pattern to the correct location on the object, the magnification of the mask pattern image projected onto the object should be changed between the beam scanning direction and the direction perpendicular thereto.
The above can be achieved by appropriately controlling the velocities of the mask and the object moved by the driving mechanism. For example, if the object is driven such that its velocity is 2% higher than that of the mask, while adjusting the projection optical system at xc3x971.01 magnification, the image of the mask pattern on the object is enlarged for 2% in the beam-scanning direction and for 1% in the direction perpendicular to the main scanning direction.
However, when the image of the mask pattern is enlarged/reduced in the beam scanning direction into a size different from that of the image magnified by the projection optical system, the mask pattern formed to the photosensitive layer on the object becomes to have blurred lines. These blurred lines are undesirable since they cause the lines obtained on the object after development and etching processes to become thinner than a required width.
The present invention is advantageous in that a projection aligner is provided that is capable of transferring an image of a pattern formed on a mask to an object at different magnifications in different directions without causing the transferred image being significantly blurred.
According to an aspect of the invention, the projection aligner transfers the image of the pattern formed on the mask to the object by scanning a light beam across the mask and the object. The projection aligner, includes a driving mechanism for synchronously moving the mask and the object to scan the light beam across the mask and the object in a predetermined beam scanning direction. The light beam scanning the mask passes through the mask and is projected onto the object by a projection optical system of which magnification is adjusted by a magnification adjusting mechanism. The magnification adjusting mechanism and the driving mechanism are controlled by a controller such that the difference between the magnification of the projection optical system and a velocity ratio of the mask and the object moved by the driving mechanism becomes below a predetermined maximum value which is determined based on a line width of the pattern formed on the mask.
For example, the controller adjusts the magnification Mgn of the projection optical system and the velocity ratio xcex1 of the mask and the object to (i) (SR1+SR2+A)/2 and (SR1+SR2xe2x88x92A)/2, respectively, when (SR1xe2x88x92SR2) greater than A, (ii) SR1 and SR2, respectively, when |SR1xe2x88x92SR2|xe2x89xa6A, and (iii) (SR1+SR2xe2x88x92A)/2 and (SR1+SR2+A)/2, respectively, when (SR1xe2x88x92SR2) less than xe2x88x92A, where SR1 and SR2 represent size ratios of the object to the mask in the beam scanning direction and a direction perpendicular to the beam scanning direction, respectively, and A represents the predetermined maximum value.
In the projection aligner configured as above, the image of the mask pattern transferred to the object does not become significantly blurred even if the image is transferred to the object with different expansion ratios in the beam scanning direction and a direction perpendicular to the beam scanning direction since the difference between the optical system magnification and the object-mask velocity ratio, which determines the degree of the blur, is kept below the predetermined maximum value.
Optionally, the projection aligner includes first and second cameras for capturing images of the object and the mask, respectively, and the controller calculates the size ratios mentioned above from the images captured by the first and second cameras. In such cases, each of the mask and the object may be provided with at least two first marks arranged thereon along the beam scanning direction and at least two second marks arranged thereon along the direction perpendicular to the beam scanning direction. If such marks are provided to the mask and the object, the controller can measure the size of each of the mask and the object in both the beam scanning direction and the direction perpendicular to the beam scanning direction based on the positions of the first and second marks in the images captured by the first and second cameras.
In some embodiments of the invention, the projection optical system includes, a lens unit having a positive power, a first mirror that deflects the light beam passed through the mask toward the lens unit, a reflector that reflects back the light beam deflected by the first mirror and passed through the lens unit, and a second mirror that deflects the light beam reflected by the reflector and passed through the lens unit toward the object. In the projection optical system configured as above, the magnification thereof can be varied by moving the reflector along an optical axis of the lens unit, and also moving the first and second mirrors toward and away from the object.